Glutaminyl cyclase (QC, EC 2.3.2.5) catalyzes the intramolecular cyclization of N-terminal glutamine residues into pyroglutamic acid (pGlu*) liberating ammonia. A QC was first isolated by Messer from the latex of the tropical plant Carica papaya in 1963 (Messer, M. (1963) Nature 4874, 1299). 24 years later, a corresponding enzymatic activity was discovered in animal pituitary (Busby, W. H. J. et al. (1987) J Biol. Chem. 262, 8532-8536; Fischer, W. H. and Spiess, J. (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 3628-3632). For the mammalian QC, the conversion of Gln into pGlu by QC could be shown for the precursors of TRH and GnRH (Busby, W. H. J. et al. (1987) J Biol. Chem. 262, 8532-8536; Fischer, W. H. and Spiess, J. (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 3628-3632). In addition, initial localization experiments of QC revealed a co-localization with its putative products of catalysis in bovine pituitary, further improving the suggested function in peptide hormone synthesis (Bockers, T. M. et al. (1995) J Neuroendocrinol 7, 445-453). In contrast, the physiological function of the plant QC is less clear. In the case of the enzyme from C. papaya, a role in the plant defense against pathogenic microorganisms was suggested (El Moussaoui, A. et al. (2001) Cell Mol Life Sci 58, 556-570). Putative QCs from other plants were identified by sequence comparisons recently (Dahl, S. W. et al. (2000) Protein Expr. Purif. 20, 27-36). The physiological function of these enzymes, however, is still ambiguous.
The QCs known from plants and animals show a strict specificity for L-Glutamine in the N-terminal position of the substrates and their kinetic behavior was found to obey the Michaelis-Menten equation (Pohl, T. et al. (1991) Proc. Natl. Acad. Sci U.S.A. 88, 10059-10063; Consalvo, A. P. et al. (1988) Anal. Biochem. 175, 131-138; Gololobov, M. Y. et al. (1996) Biol. Chem. Hoppe Seyler 377, 395-398). A comparison of the primary structures of the QCs from C. papaya and that of the highly conserved QC from mammals, however, did not reveal any sequence homology (Dahl, S. W. et al. (2000) Protein Expr. Purif. 20, 27-36). Whereas the plant QCs appear to belong to a new enzyme family (Dahl, S. W. et al. (2000) Protein Expr. Purif. 20, 27-36), the mammalian QCs were found to have a pronounced sequence homology to bacterial aminopeptidases (Bateman, R. C. et al. (2001) Biochemistry 40, 11246-11250), leading to the conclusion that the QCs from plants and animals have different evolutionary origins.
Recently, it was shown that recombinant human QC as well as QC-activity from brain extracts catalyze both, the N-terminal glutaminyl as well as glutamate cyclization. Most striking is the finding, that cyclase-catalyzed Glu1-conversion is favored around pH 6.0 while Gln1-conversion to pGlu-derivatives occurs with a pH-optimum of around 8.0 (Schilling et al. (2004), FEBS-Letters 563 (1-3) 191-196). Since the formation of pGlu-Aβ-related peptides can be suppressed by inhibition of recombinant human QC and QC-activity from pig pituitary extracts, the enzyme QC is a target in drug development for treatment of Alzheimer's disease (Schilling et al. (2008), Nature Medicine 14, 1106-1111).
Moreover, it was shown recently in WO 2008/034891 that isoenzymes of QC exist, designated as “isoQC” or “QPCTL”.
Chemotactic cytokines (chemokines) are proteins that attract and activate leukocytes and are thought to play a fundamental role in inflammation. Chemokines are divided into four groups categorized by the appearance of N-terminal cysteine residues (“C”-; “CC”-; “CXC”- and “CX3C”-chemokines). “CXC”-chemokines preferentially act on neutrophils. In contrast, “CC”-chemokines attract preferentially monocytes to sites of inflammation. Monocyte infiltration is considered to be a key event in a number of disease conditions (Gerard, C. and Rollins, B. J. (2001) Nat. Immunol. 2, 108-115; Bhatia, M., et al. (2005) Pancreatology. 5, 132-144; Kitamoto, S., Egashira, K., and Takeshita, A. (2003) J Pharmacol. Sci. 91, 192-196). The MCP family, as one family of chemokines, consists of four members (MCP-1 to 4), displaying a preference for attracting monocytes but showing differences in their potential (Luini, W., et al. (1994) Cytokine 6, 28-31; Uguccioni, M., et al. (1995) Eur. J Immunol. 25, 64-68).
A number of studies have underlined in particular the crucial role of MCP-1 for the development of atherosclerosis (Gu, L., et al. (1998) Mol. Cell 2, 275-281; Gosling, J., et al. (1999) J Clin. Invest. 103, 773-778); rheumatoid arthritis (Gong, J. H., et al. (1997) J Exp. Med. 186, 131-137; Ogata, H., et al. (1997) J Pathol. 182, 106-114); pancreatitis (Bhatia, M., et al. (2005) Am. J Physiol. Gastrointest. Liver Physiol 288, G1259-G1265); Alzheimer's disease (Yamamoto, M., et al. (2005) Am. J Pathol. 166, 1475-1485); lung fibrosis (Inoshima, I., et al. (2004) Am. J Physiol Lung Cell Mol. Physiol 286, L1038-L1044); renal fibrosis (Wada, T., et al. (2004) J Am. Soc. Nephrol. 15, 940-948), and graft rejection (Saiura, A., et al. (2004) Arterioscler. Thromb. Vasc. Biol. 24, 1886-1890). Furthermore, MCP-1 might also play a role in gestosis (Katabuchi, H., et al. (2003) Med. Electron Microsc. 36, 253-262), as a paracrine factor in tumor development (Ohta, M., et al. (2003) Int. J Oncol. 22, 773-778; Li, S., et al. (2005) J Exp. Med 202, 617-624), neuropathic pain (White, F. A., et al. (2005) Proc. Natl. Acad. Sci. U.S.A) and AIDS (Park, I. W., Wang, J. F., and Groopman, J. E. (2001) Blood 97, 352-358; Coll, B., et al. (2006) Cytokine 34, 51-55).
The mature form of human and rodent MCP-1 is posttranslationally modified by Glutaminyl Cyclase (QC) to possess an N-terminal pyroglutamyl (pGlu) residue. The N-terminal pGlu modification makes the protein resistant against N-terminal degradation by aminopeptidases, which is of importance, since chemotactic potency of MCP-1 is mediated by its N-terminus (Van Damme, J., et al. (1999) Chem. Immunol. 72, 42-56). Artificial elongation or degradation leads to a loss of function although MCP-1 still binds to its receptor (CCR2) (Proost, P., et al. (1998), J Immunol. 160, 4034-4041; Zhang, Y. J., et al. 1994, J Biol. Chem. 269, 15918-15924; Masure, S., et al. 1995, J Interferon Cytokine Res. 15, 955-963; Hemmerich, S., et al. (1999) Biochemistry 38, 13013-13025).
Due to the major role of MCP-1 in a number of disease conditions, an anti-MCP-1 strategy is required. Therefore, small orally available compounds inhibiting the action of MCP-1 are promising candidates for a drug development. Such compounds are, for instance, inhibitors of QC as shown in WO 2008/104580.
Atherosclerotic lesions, which limit or obstruct coronary blood flow, are the major cause of ischemic heart disease related mortality, resulting in 500,000-600,000 deaths annually. Percutaneous transluminal coronary angioplasty (PTCA) to open the obstructed artery was performed in over 550,000 patients in the U.S. and 945,000+ patients worldwide in 1996 (Lemaitre et al. 1996). A major limitation of this technique is the problem of post-PTCA closure of the vessel, both immediately after PTCA (acute occlusion) and in the long term (restenosis): 30% of patients with subtotal lesions and 50% of patients with chronic total lesions will progress to restenosis after angioplasty. Additionally, restenosis is a significant problem in patients undergoing saphenous vein bypass graft. The mechanism of acute occlusion appears to involve several factors and may result from vascular recoil with resultant closure of the artery and/or deposition of blood platelets along the damaged length of the newly opened blood vessel followed by formation of a fibrin/red blood cell thrombus.
Restenosis after angioplasty is a more gradual process and involves initial formation of a subcritical thrombosis with release from adherent platelets of cell derived growth factors with subsequent proliferation of intimal smooth muscle cells and local infiltration of inflammatory cells contributing to vascular hyperplasia. It is important to note that multiple processes, among which thrombosis, cell proliferation, cell migration and inflammation each seem to contribute to the restenotic process.
In the U.S.A., a 30-50% restenosis rate translates to 120,000-200,000 U.S. patients at risk from restenosis. If only 80% of such patients elect repeated angioplasty (with the remaining 20% electing coronary artery bypass graft) and this is added to the costs of coronary artery bypass graft for the remaining 20%, the total costs for restenosis tretment easily amounts to billions of dollars in the U.S. Thus, successful prevention of restenosis could result not only in significant therapeutic benefit but also in significant health care savings.
As outlined above, monocyte chemoattractant protein 1 (MCP-1, CCL2) belongs to a family of potent chemotactic cytokines (CC chemokines), that regulate the trafficking of leukocytes, especially monocytes, macrophages and T-cells, to sites of inflammation (Charo, I. F. and Taubman, M. B. (2004) Circ. Res. 95, 858-866). Besides its role in, e.g. vascular diseases, compelling evidence points to a role of MCP-1 in Alzheimer's disease (AD) (Xia, M. Q. and Hyman, B. T. (1999) J Neurovirol. 5, 32-41). The presence of MCP-1 in senile plaques and in reactive microglia, the residential macrophages of the CNS have been observed in brains of patients suffering from AD (Ishizuka, K., et al. (1997) Psychiatry Clin. Neurosci. 51, 135-138). Stimulation of monocytes and microglia with Amyloid-β protein (Aβ) induces chemokine secretion in vitro (Meda, L., et al. (1996) J Immunol. 157, 1213-1218; Szczepanik, A. M., et al. (2001) J Neuroimmunol. 113, 49-62) and intracerebroventricular infusion of Aβ(1-42) into murine hippocampus significantly increases MCP-1 in vivo. Moreover, Aβ deposits attract and activate microglial cells and force them to produce inflammatory mediators such as MCP-1, which in turn leads to a feed back to induce further chemotaxis, activation and tissue damage. At the site of Aβ deposition, activated microglia also phagocytose Aβ peptides leading to an amplified activation (Rogers, J. and Lue, L. F. (2001) Neurochem. Int. 39, 333-340).
Examination of chemokine expression in a 3×Tg mouse model for AD revealed that neuronal inflammation precedes plaque formation and MCP-1 is upregulated by a factor of 11. Furthermore, the upregulation of MCP-1 seems to correlate with the occurrence of first intracellular Aβ deposits (Janelsins, M. C., et al. (2005) J Neuroinflammation. 2, 23). Cross-breeding of the Tg2576 mouse model for AD with a MCP-1 overexpressing mouse model has shown an increased microglia accumulation around Aβ deposits and that this accumulation was accompanied by increased amount of diffuse plaques compared to single-transgenic Tg2576 littermates (Yamamoto, M., et al. (2005) Am. J Pathol. 166, 1475-1485).
MCP-1 levels are increased in CSF of AD patients and patients showing mild cognitive impairment (MCI) (Galimberti, D., et al. (2006) Arch. Neurol. 63, 538-543). Furthermore, MCP-1 shows an increased level in serum of patients with MCI and early AD (Clerici, F., et al. (2006) Neurobiol. Aging 27, 1763-1768).
Osteoporosis is a disease of bone loss, typically as a result of estrogen depletion. The process of osteoclastogenesis plays a central role in osteoporosis. Osteoclastogenesis is a multistep event involving not only the proliferation of preosteoclasts from the monocyte and macrophage linage but also their differentiation into osteoclasts. Enhanced osteoclast activity is the main reason for bone loss mediated by estrogen deficiency. Binder et al. have shown that the chemokine recepter CCR2 is involved in the pathomechanisms leading to postmenopausal osteoporosis. Ccr2−/− mice were protected from estrogen deficiency-mediated bone loss, and this effect was mediated via osteoclasts (Binder et al., (2009) Nat Med. April; 15(4), 417-24). Moreover, estrogen was also shown to downregulate MCP-1, and studies comparing pre- and post-menopausal women showed that there is increased expression of MCP-1 in the latter group. Binder et al. further found that MCP-1 deficient mice show only an intermediate bone phenotype, i.e. that MCP-1 is not the only ligand for CCR2 playing a role in osteoporosis. They showed that MCP-3, which is also a ligand of CCR2, has similar pro-osteoclastogenic effects in presence of CCR2 and can substitute for MCP-1 (Binder et al., (2009) Nat Med. April; 15(4), 417-24).